This invention relates to an improved heat exchanger construction which provides increased heat transfer in either direction between the fluid within a tube and the outer surface of the tube. The particular type of heat exchanger disclosed herein comprises a plurality of parallel fluid-carrying tubes arranged in cylindrical fashion, the tubes having a series of thin sheet metal annular fins closely spaced along their length to enhance the heat exchanging efficiency. Each fin is provided with punched holes to receive an array of tubes. This type of heat exchanger may be mounted for rotation about the axis of the fins, with the rotation establishing an axial air flow into the center of the array and then radially outwardly over the surface of the tubes and fins. Examples of this type of heat exchanger may be found in U.S. Pat. Nos. 3,189,262 and 3,347,059. The same shaped annular fin construction is shown in U.S. Pat. No. 4,005,748.
The invention disclosed herein is directed to an improvement in heat exchange efficiency provided by internal fins within each of the heat exchanger tubes. The prior art has employed a variety of techniques for constructing an internally-finned tube. Prior art of which Applicants are aware is exemplified by U.S. Pat. Nos. 349,060; 2,032,134; 2,079,144; 2,445,471; 3,005,036; 3,200,848; 3,208,131; 3,359,616; 3,473,348; and 3,773,106. However, Applicants have encountered substantial problems in attempting to design and construct an efficient internally finned tube which can be economically manufactured and which assures proper heat transfer between the internal fins and the tube wall.
Such a tube should have minimum wall and fin thickness, to reduce the weight and cost of material and to facilitate heat transfer. There must be a firm and solid connection between the fins and the inner surface of the tube wall, so that heat will flow across such joint without any insulating gaps. Such a tube must also be compatible with high production techniques, with a minimum of handling and labor required for its fabrication.
Accordingly, it is the principal object of this invention to provide an internally finned tube for a heat exchanger which satisfies all of the above criteria.